A problem which is common to military and to search-and-rescue operations is the need to quickly identify the location of a source of electromagnetic (EM) radiation. In the context of search-and-rescue, the person sought will often have a portable cellular telephone with which communication is possible, but the person in need of rescue may not know his location or will not be able to adequately articulate it. Since cell-phone batteries often provide a limited amount of active cell-phone operation, especially when the battery is near the end of its life, or when it has not been charged in some time, a limited amount of time may be available in which the cell-phone can be used as an electromagnetic source for traditional triangulation or other locating techniques. In a military scenario, the electromagnetic emitter may be actively attempting to avoid being located. One way to reduce the likelihood of being located is to terminate the transmission as quickly as possible. Thus, there are scenarios in which rapid geolocation of an electromagnetic radiator or emitter is desired.
The problem of geolocation in a timely fashion is extremely difficult due to the complex propagation of electromagnetic energy in environments in which these types of radios are typically used. It can be expected that when rapid geolocation is required, the rural environment will include hills, mountains, and possibly vegetation and structures, while the urban environment will include many structures and reflective objects, both fixed and moving. The reflections due to structures and terrain features, in turn, result in random signal amplitude variations known as fading as the reflections add and subtract at the receiving site.
FIG. 1 is a simplified representation of a portion of a generally flat urban environment 10 including several buildings designated 12, 14, and 16, and two mutually crossing roads 22 and 24. There is a need for a geolocation system which is capable of rapidly identifying the location of a source of electromagnetic radiation. An asterisk (*) 30 at the top of building 14 has been arbitrarily selected to represent the location of an electromagnetic transmitter which is to be geolocated or to have its location determined by remote measurements at locations 20 (a, b, c and d). Note that location 20d is shown as being a vehicle, thereby illustrating that the measurements can be achieved on the move.